This invention relates to a circuit operable in one mode as a high voltage level shifting inverter and in other modes as a low power clamp to one or the other of two power supply lines.
In some applications it is desirable that a circuit be capable of performing more than one function. This has the advantage of reducing the number of components needed to perform the necessary functions. However, the circuit then has an even greater than usual number of constraints to overcome. For example, a driver circuit for a high density electrically alterable memory array must be able to operate at, and provide, relatively high voltages when information is being written into the array while operating at lower voltages when information is being read out of the memory.
In high density arrays arranged in rows and columns, the driver circuit must be of the type that can be fabricated on "pitch" (i.e. in line) with the rows or columns of the array. Where the driver circuit must operate at high voltages this presents a problem since high voltage devices normally require much space. In addition, where the memory array is of the programmable type, having devices which can be set to different conditions, the driver circuit must be capable of producing the voltages necessary to generate these different conditions.
Accordingly, a circuit embodying the invention is operable in one mode as a high voltage level shift inverter and in other modes as a low power clamp to one or the others of two voltage rails.